About one month after I
completed the extraction and re-installation of the PSD from my truck,
necessitated to replace a rusted out oil pan, I noticed diesel fuel on the floor
of my garage under the rear of my truck. Sure enough the steel rear fuel
tank had also rusted through. Why in the world Ford ever put a poly
midship tank in, and a STEEL rear tank, I'll never figure out. So, I
contacted Mike at MTS Company, www.mtscompany.com, and ordered a replacement poly rear fuel tank. I
figured that since I would have the tank off of the truck, I might as well do
the Fuel Tank Vent Mod that has been talked about in the '94-'97 TDS.com forums. I grabbed the digital camera and went
to work.

Overview of Project

Ford installed a roll-over
valve on the top of the fuel tanks that has a small 1/4" rubber hose that has a
vented cap and is clipped to the frame. The roll-over valve's
purpose is to prevent fuel from escaping out of the vent in case the vehicle
rolls over. There is also a rubber hose inside of the filler neck that the
fuel actually goes through to get into the fuel tank. The steel filler
neck and rubber hose you see by crawling under the truck are merely channeling
air between them and the internal rubber hose to let air escape from the tank as
it is being filled with fuel. This system can definitely be improved upon.

The Fuel Tank Vent Mod uses
the roll-over valve attached to a larger diameter fuel line that runs from the
fuel tank to a fitting installed on the steel filler neck. This assists in evacuating
air from the tank during re-fueling. The fuel cap is designed to vent
naturally, so there should not be a pressure problem within the tank. The
fuel line connecting the tank to the filler neck will contain any fuel should
there be a roll-over situation.

The installation of the
new Ford roll-over valves and the modification of the steel filler necks are exactly the same on the front and
rear, so what I have described below applies to both. Just getting access
to the top of the tanks to do the work is different.

Materials Used

1)
Approximately 7 1/2' of 5/8" fuel line. I used 3' for the front vent, and
4 1/2' for the rear vent. I obtained my fuel line from NAPA, #H-183, for $17
including 4 hose clamps, #705-1313.

4)
2 - Ford valve grommets, #F6TZ-9B076-AA, $3.99 each, plus shipping. You can
probably use the existing grommets as I saw no difference when compared to the
new ones.

5) Fresh
pack of JB Weld, $3.97.

Total cost of project is about
$65.

Modifying the steel filler neck

Unscrew the three 7 mm
hex head screws holding the filler neck to the bed, located around the fuel
filler cap. Unscrew the two hose clamps where the steel filler neck meets
the rubber neck, and gently pull the steel neck out away from the rubber neck.
In doing so, you are also removing a long rubber hose that is attached to the
inside of the steel filler neck, that goes through the rubber filler tube into
the tank. Keep pulling as it's longer than you'd expect. You will be
removing and discarding the rubber hose and internal steel fitting in the
following procedure:

With the filler neck out of the truck, clamp it in a vise,
carefully, as not to crush it. Use a long screwdriver in the fuel cap
end and begin tapping on the ring inside the filler neck that has small
crescent shaped holes visible as you look down into the filler neck.
Tap with a hammer and pull on the hose sticking out the other end. The
object is to get the steel insert part with the crescent shaped holes all
the way to the other end of the steel tube.

With the steel insert and rubber hose at the bottom end
of the filler neck, grab the rubber hose firmly and pull it off of the steel
insert. Next, grab the steel insert with vise grips to hold
it and use a
reciprocating saw to cut a slot in one side of the insert.

Using the vise grips and a screwdriver, pry on the insert
to try and fold it in on itself and pull it out the end of the filler neck.

There is a dimple in the side of the steel filler neck
just below the mounting plate that works well for locating where to install
the hose barb. I used the largest drill bit I had then carefully reamed
the hole by hand to get the hole just the right size to thread the 1/2"
brass hose barb into the hole. You only want to go 2 turns or so
into the filler neck so that the fitting does not interfere with the fuel filler
nozzle when fueling. JB Weld the fitting into place.

Installing the new Ford
roll-over valves

The front valve
is really easy to do. Stick your head up under the bed in front of the
driver's side rear tire and look at the top of the tank. You will see where the fuel
lines go into the tank and rearward of that is the grossly inadequate roll over
valve/vent with a small rubber tube that is clipped to the frame rail. You
should be able just to reach in there and wiggle the valve out of the rubber
grommet, and unclip the rubber hose from the frame rail. The rear vent
will require dropping the tank to get at it. I would recommend removing
the tank completely, install the new vent tube onto the tank, then re-install
the tank, rather than try to struggle with the tank hanging there. To do
the rear tank, remove
the spare tire, remove 1/2 of the skid/mounting plate, place a jack under the
exposed half of the tank, then remove the other plate. It helps to have an
assistant, but it's do-able by yourself with the proper equipment.

For the front tank, attach one end of the 5/8" fuel
line to the new roll-over valve with a hose clamp. Replace the grommet
with the new one, if you so desire. Reach up on
top of the tank and insert the barb into the tank with the fuel line
perpendicular to the frame rail. It's helpful to add some lubricant to
the grommet and the valve to help the valve slip into position. Re-install the filler neck onto
the truck, install the three 7 mm screws before the hose clamps, but
after the steel tube is fitted inside the rubber hose.

Front tank vent mounted.

Then, run the 5/8" fuel line up to the barb on the filler
neck, cut to length, and install with a hose clamp. I used a zip tie
to hold the new hose in place using the hole in the bed support, making sure
that the hose slopes FROM the filler neck TO the tank. If you do not do
this, the fuel line will create a trap and fuel will sit in the trap and the
mod will be worse than when you started. You're done with the front.

Front filler neck attached.

Install the remainder of the 5/8" fuel line to the
other new roll-over valve with a hose clamp, and insert it into the grommet
in the fuel tank. Again, some lubrication would help. Then, re-install the tank, routing the 5/8" fuel
line perpendicular to the frame rail so it comes out by the filler neck.

Rear tank assembly.

Re-install the filler neck onto the truck, again start
with the three 7mm screws after the steel is fitted into the rubber hose.
Cut any excess off of the 5/8" fuel line, and install onto barb with a
hose clamp. Make sure the fuel line runs FROM the filler neck TO the tank,
zip tie as needed, and you're done.

Rear filler neck attached.

Results

I was a little peeved after
completing the project because there was a leak around the sending unit on the
tank, and when I filled it up, I had diesel fuel pouring out the top of the
tank. So I needed to pull the tank and re-seal the gasket on the sending
unit.

Anyway, I went to the 'Big
Truck' pump to fill up and was totally NOT impressed. It actually seemed
like it took longer to fill up as the nozzle kept clicking off. However, I
still have to use the 'Little Truck' pump for the real test since the fuel
coming out of the 'Big Truck' pump just gushes out. All in all, I'd do
this mod again as it's not really that difficult, and didn't cost that much.

I
found out, through other posts online
that you should not use the 90 degree street elbow on the filler neck, only the
hose barb. What was happening was the fuel line would dip, creating a trap and
collecting fuel and no air at all was getting into the tank. After eliminating
the 90 degree street elbows the system works great! I am pleased.